A central problem for theories of memory development is how the superior memory of children and adults evolves from the memory abilities of infants. Currently, the paucity of data on infant long-term memory precludes a solution. In the last funding period, we obtained the first systematic data describing the ontogeny of infant long-term memory from 2 to 18 months of age and its specificity from 2 to 12 months. We also began characterizing effective memory reactivation (reminder) treatments from 3 to 12 months and demonstrated that memories acquired at 2 to 6 months could be maintained over significant periods of development by periodic nonverbal reminders: either reinstatement or reactivation treatments, which were originally developed with immature animals. Which reminder was most effective, however depended on the state of the memory: Reinstatement was more effective when the memory was active, and reactivation was more effective when it was not. This proposal asks two fundamental questions: What are the characteristics of effective reminders for infants? And how do they work? To answer them, we will systematically examine the "nuts and bolts" of these two reminder procedures with infants of different age, characterizing effective reactivation and reinstatement reminders and documenting for each type the effect of reminder number and spacing on the persistence and specificity of memories, the consequences of reminding at different points on the forgetting function, how different memories interact during reminding, and if and how memories are distorted over the course of reminding, etc. Our research uses a standardized operant conditioning procedure. During training in their own homes, infants learn to activate a particular mobile or miniature train in a particular context. During reminding, they receive brief reinstatements (periodic partial training episode) or reactivation treatments (exposure to an isolated component of original training). During the long-term retention test, they are shown an object that is the same as or different from the training object and indicate whether or not they recognize it by responding above baseline. Reminder controls receive the same reminder regimen without prior training. This research will solve the central problem, revealing how the effects of early experiences endure and contribute to an individual's growing knowledge base. In addition, the findings will establish an important database for research into the brain mechanisms that underlie early memory development, extending the breadth and generality of earlier reminder studies with animals. These findings will offer new insights into how re-encoding, storage, and retrieval mechanisms are implicated in reminding. They will also shed light on whether reactivation and reinstatement engage the same underlying process or different processes. Finally, they will significantly advance our understanding of the normal development and structure of early cognition. From a mental health perspective, the findings will provide interventions that can alleviate learning/memory deficits of individuals of any age who require remediation and can enhance the learning/retention of individuals who do not.